From neighboring Somalia, spokesman Sheik Ali Mohamud Rage for al-Shabab — the militant group that claimed responsibility for the attack — said in an audio file posted on a website that the hostage takers had been ordered to "take punitive action against the hostages" if force was used to try to rescue them.

...

Al-Shabab said on a Twitter feed, an account that unlike some others appears to be genuine, that the attackers had lots of ammunition. The feed said that Kenya's government would be responsible for any loss of hostages' lives.

And from The Globe and Mail:

Kenyan security forces were in the final stages of flushing out Islamist extremist terrorists from a besieged shopping mall, the Vice-President said late Monday, two days after the upscale mall was seized by members of a Somali group linked to al-Qaeda.